This invention relates to a beam splitter for use in splitting a single incident light beam into a plurality of outgoing light beams substantially parallel to one another.
In U.S. Pat. No. 4,125,864 issued to John E. Aughton, a beam splitter is disclosed which splits a single incident light beams into a plurality of outgoing light beams substantially parallel to one another. As will later be described in conjunction with one of the accompanying figures of the drawing, the beam splitter comprises a transparent substrate or block having a pair of parallel planes, an antireflection layer at an incident portion defined on one of the planes, a reflection layer laterally adjacent to the antireflection layer on the one plane, and a semitransparent layer divided into a plurality of partial semitransparent layers at outgoing portions defined on the other plane. With this beam splitter, each of the outgoing light beams should exit through each of the partial semitransparent layers predetermined for each outgoing light beam. Stated otherwise, the partial semitransparent layers are in one-to-one correspondence to the outgoing light beams. Therefore, the partial semitransparent layers must exactly be positioned or registered on the outgoing portions of the other plane. Inasmuch as a very small distance is required between two adjacent ones of the outgoing light beams, it is difficult to precisely register the partial semitransparent layers in place.
Herein, it is to be noted here that each of the partial semitransparent layers should have a reflectance different from one another so as to keep the luminous energy of each outgoing light beam at a desired value. Each partial semitransparent layer is manufactured by stacking a plurality of dielectric films on one another. The number of the dielectric films must be varied at every outgoing portion in order to provide each reflectance different from one another. It is very troublesome to deposit the above-mentioned partial semitransparent layers on the respective outgoing portions. A reduction of a yield inescapably takes place in manufacturing the beam splitter because of such a troublesome process.